Upload
bowie
View
28
Download
0
Tags:
Embed Size (px)
DESCRIPTION
BoNuS: Radial-Drift TPC using Curved GEMs. A Time Projection Chamber having Radial Drift Direction, based on GEMs which have been Curved to form cylinders. Howard Fenker a * , Jefferson Lab. Hall-C Collaborators indicated by bold type. - PowerPoint PPT Presentation
Citation preview
BoNuS: Radial-Drift TPC using Curved GEMsA Time Projection Chamber having
Radial Drift Direction, based on
GEMs which have been Curved to form cylinders.
Howard Fenkera*, Jefferson Lab
N. Baillieb, P. Bradshawc, S. Bueltmannc, V. Burkherta, M. Christyd, G. Dodgec, D. Duttae, R. Enta,J. Evansb, R. Ferschb, K. Giovanettif, K. Griffioenb, M. Ispiryang, C. Jayalathd, N. Kalantariansg, C. Keppeld, S. Kuhnc, G. Niculescuf, I. Niculescuf, S. Tkachenkoc, V. Tvaskisd, J. Zhangc
Graduate Student Undergraduate a Thomas Jefferson National Accelerator Facility (Jlab)b College of William and Mary
c Old Dominion Universityd Hampton Universitye Tri-Universities Nuclear Lab (TUNL)f James Madison Universityg University of Houston
* This work was partially supported by DOE Contract No. DE-AC05-84ER40150 under which the Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility (Jefferson Lab).
Hall-C Collaborators indicated by bold type
MotivationPR-97-107
“LENT”
Motivation
• Purpose– Provide almost-free neutron
target to improve our understanding of neutron structure.
• Purpose– Neutron Structure-function
measurements unencumbered by Final-State Interaction Effects
BoNuS Experiment - Structure Functions
Ratio F2n/F2
p vs.x. The small data points indicate the expected results of the BONUS experiment for several different bins in Q2 with statistical error bars. Estimated systematic errors due to experimental and theoretical uncertainties are indicated by the band at the bottom (total systematic error / point-to-point error after normalization at low x). Arrows indicate the different possible approaches to the limit x->1. The shaded area indicates the range of uncertainty from existing data due to different treatment of nuclear effects.
Method
• Measure slow protons– Identify spectator
protons to tag e-d events in which the neutron was struck.
np
e
before
e
p
?
after
n
Spectator Proton Characteristics
– Angular distribution is isotropic. Backwards proton almost certain to be a spectator.
– Momentum distribution favors low values.
– Tracks are 20x - 50x minimum ionizing.
dE/dx is HIGH for slow protons
Tells us two things:
1. Protons easy to identify
2. Detector must be thin
Tracking a low energy, heavily-ionizing particle requires a low-mass detector
• Time Projection Chamber (TPC)– Just a box of gas– Readout elements
only on the surfaces.– Windows can be
made thin.– Information density is high, but each channel of readout
may need to record an entire waveform for several s -- like having an oscilloscope per channel!
Cathode Anode Readout
BoNuS is just a curled-up TPC.
For convenience, the gas-gain elements are GEMs.
GEM Readout
• http://gdd.web.cern.ch/GDD
Studies w/flat prototype
• Uses standard 10cm x 10cm GEMs.• Drift region similar to planned final detector.• Uses 3x 3M GEMs to allow tracking cosmics (min-I).
• At present, tests are performed using 80/20 Ar/CO2.
Drift Plane (Cathode board + foil)
SegmentedCathode
GEM Foils
5/16 in 1.90 cm.
0.46 cm.
• Cosmic tracks easily recognized.
• Position resolution would be better with charge sharing over ≥3 pads.
• Gain ~ 303
drift
xpad #
xpad #
drift
20mm x 19mm 20mm x 19mm
20mm x 19mm 20mm x 19mm
box size represents Q(x,t)
Cosmic Studies w/flat prototype
• Heavily Ionizing Protons from TUNL’s Tandem
Proton Studies w/flat prototype
Curved GEM for Prototype
Curved prototype RTPC
Cosmic event from Curved GEM TPC
BoNuS RTPC: Exploded View
Inserting Pre-amp cards
BoNuS Readout Crate
What it really looks like
A Way to Mount Everything
Tracks are Pretty Obvious
Remember: we are working in 3D. That helps!
Results are Making Sense
Vertex position agreement between CLAS and BoNuS:
Angle measurementsagree, too.
Measured dE/dx vs. P
proton / deuteron / 3He / 4HeCurves: Bethe-Bloch Formula:
Particle ID via dE/dx
After determining track momentum p, histogram the ratio:
dEdx measured
dEdx p
Bethe Bloch
under the assumption that the particle was a proton.
NIM article to be submitted soon:
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
W (GeV/c2)
100
200
300
400
500
600
700
800
900
BoNuS Physics AnalysisBoNuS Physics Analysis
Ebeam = 4.223 GeV N. Baillie
Recoil mass with and w/o using measured ps momentum.
Status of BoNuS Analysis
n
np
CLAS
RTPC
N
N
)(
model for σn/σD by P. Bosted
BoNuS: Next 6 GeV/c Experiment
BoNuS: 12 GeV/c Experiment
Conclusion
• Specialized spectator proton detector developed
• First use of GEMs at JLab
• First application of Curved GEMs
• Experiment Run
• More to come